Principles of direct coupling The following table explains various basic principles of direct galvanic coupling:
Application
Principle of coupling
Single-wire lines or pipes (with or
without insulation against earthing)
The distance between the earth spike and
the ends of the connected lines should be
as great as possible.
There is a danger of the return current
flowing through the earth into adjacent
lines, which could result in their path
being followed.
Single-wire cable with metallic screen
and earthing insulation
Short circuit between internal conductor
and screen at the end of the cable with
earthing at the beginning and end of the
cable as well.
If the earth connections made are
unfavourable, the current in the
internal conductor and the return
current in the screen will cancel each
other out. Under certain
circumstances this can prevent the
cable from being detected.
Alternatively, a connection without an
earth connection can also be made.
Multiple-wire cable (internal conductor
connected or disconnected) with
metallic screen and earthing insulation
Same application as in example 1.
Metallic conduit (with or without
insulation against earthing)
The earth spike and the conduit should be
spaced as far apart as possible. Under
certain circumstances, optimum
positioning of the earth spike may require
several attempts.
If a return wire is available
The spacing of the return wire should
correspond to at least 10 times the depth
of the line being located.
Pair of wires (with or without screen)
with short circuit at the end of the cable
For twisted pairs of wires (with a
length of lay of the twist greater or
equal to the laying depth), the
orientation of the cable can be easily
determined.
Adjacent lines which are
horizontal
to
each other
Minimum of the reception signal
Lines situated on top of each other
vertically
Maximum of the reception signal
3
2
1
4
5
6
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